We don't really know the reason behind the apps suddenly going Free, and none of the apps also give an explanation on the App Store listing. However, it wouldn’t be outlandish to believe that this is somehow related to the Apple App Store’s fifth anniversary, and could be a part of the celebrations.

The company, however, has not released any official statement yet, regarding these apps. If indeed these are related to the fifth anniversary, we could see more apps added to the list of free apps.